(1) Field of the Invention
The present invention relates to a closure mechanism for a loose-leaf holder for sheets defining holes along an edge thereof, comprising a base plate having flaps stamped out of the base plate and bent upwardly about a common axis, fixed prongs for receiving the holes of the sheets fastened to the base plate along an edge of the base plate, commonly pivotal prongs along an opposite base plate edge and having a loop portion cooperating with the fixed prongs upon pivoting the prongs into engagement with the fixed prongs, and a common carrier plate for the pivotal prongs, the carrier plate defining slots receiving the base plate flaps with slight play, the common axis of the flaps extending substantially parallel to a connecting line between the pivotal prongs whereby the common carrier plate with the pivotal prongs is mounted on the base plate for pivoting about the common axis.
(2) Description of the Prior Art
Such a closure mechanism has been disclosed, for example, in German Pat. No. 816,689. The base plate disclosed in this patent has a flat surface, except for two small flaps pivotally mounting the carrier plate on the base plate and an upwardly bent flap supporting an actuating lever of the closure mechanism. The carrier plate for the pivotal prongs is also substantially flat, the carrier plate defining the slots wherein the base plate flaps are engaged. To secure the carrier plate on the base plate, the base plate flaps have bent-over upper ends holding the carrier plate. This, however, does not safely hold the carrier plate on the base plate. Furthermore, the bent-over flaps interfere with the pivoting motion of the carrier plate, particularly if the upper flap ends are bent over to enclose an angle of the order of magnitude of 90.degree. with the base plate in an effort to increase the safety of the connection between the base and carrier plates whereby the play between the carrier plate and the inside of the bent-over flaps is reduced to a minimum. Thus, the safety of the interconnection between the base and carrier plates is proportional to a reduction in the pivoting range of the carrier plate on the base plate. Therefore, the closure mechanism must be manufactured with very close tolerances, which are difficult to attain. In this respect, it must be noted that the flaps are subjected to inner tensions when they are stamped out of the base plate and bent upwardly, which makes the maintenance of the required close tolerances even more difficult.